Investigative ophthalmology & visual science
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Invest. Ophthalmol. Vis. Sci. · Nov 1990
Shedding of rod outer segments is light-driven in goldfish.
Rod outer segment (ROS) shedding in goldfish was quantified by measuring the number of phagosomes in the retinas of goldfish that were maintained under natural or artificial cyclic light, constant light, or constant dark conditions. Fish maintained in cyclic light, whether natural or artificial, had robust daily rhythms of ROS shedding. The ROS tips were shed primarily during the light phase of the cycle, and maximum shedding occurred 2-4 hours into the light period. ⋯ Placing fish in darkness for 0.5 hours did not induce shedding, nor did placing them in darkness for 3 hours without returning them to light. ROS shedding thus appears to be goldfish is completely dependent on changes in ambient illumination; no circadian or endogenous components were found. Previous observations of circadian changes in behavioral visual sensitivity therefore cannot be due to endogenous changes in ROS length.
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To investigate the autonomic components of the pupillary light reflex in humans, we used infrared pupillometry combined with a partial local cholinergic (tropicamide) or alpha-adrenergic (thymoxamine) blockade. The pupillary response curve was analyzed using parameters identical or similar to those employed previously to study the autonomic components of the pupillary light reflex. ⋯ We found the expected cholinergic contribution to the constrictive phase of the pupillary light reflex but no evidence for peripheral alpha-adrenergic activity during redilation. We propose that redilation primarily involves parasympathetic relaxation, modulated by cholinergic inhibition of the dilator muscle and central sympathetic inhibition of the Edinger-Westphal nucleus.
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Eye movements that accompany a blink have been measured in human subjects by the use of a visual-persistence method. With straight-ahead binocular viewing, each eye typically rotates nasalward and downward 1-2 deg during the closing phase of a blink. These eye movements are more rapid than the lid movements as recorded by high-speed photography. ⋯ Sequential photography of the cornea in profile reveals that the eye moves inward and back out again during a blink. The amplitude of this retraction is typically less than 1 mm; and its time course, slower than that of the rotational eye movements, parallels the closure and opening of the lids. In normal conditions of viewing there is no evidence of conjugate saccades, or of any large, upward rotation of the eyes (Bell's phenomenon) that was once believed to take place during a blink.
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The pupillary light reflex of 15 strabismic and anisometropic amblyopes, and eight subjects who had recovered from functional amblyopia was studied by using an infrared electropupillogram. Ten of the fifteen amblyopes had significantly longer latencies of contraction when the amblyopic eyes were stimulated than when the normal eyes were stimulated. ⋯ All of the subjects who had recovered showed no significant difference of the latencies of the pupillary responses to stimulation between normal and amblyopic eyes. These findings indicate that a retinal mechanism in amblyopic eyes may be responsible for the abnormally long pupillary light reflex latency.